Lighting amount and intensity. - The Planted Tank Forum
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post #1 of 7 (permalink) Old 01-18-2007, 10:50 PM Thread Starter
Algae Grower
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Lighting amount and intensity.

I am curious to the thought of lighting for a tank. I have a 125 gallon, 4x2x2. I am using 5 bulbs, and until recently they were only inches from the surface of the water. I built a new canopy and now the bulbs are about a foot above the water surface. My plants do not bubble as much as before, but the algae is not as bad.

Is there a relation or equation for this sort of thing? I have 2 bulbs currently that are not the most intense bulbs, and I am thinking of swapping them out for the more intense lifeglows I have (they are 6500K but put out 330 lux a bulb. They are bright). Does distance from the tank matter, and if so, how much? I realize being too far away is bad, as is too close, but is there a way to find the happy medium? It is not so easy to fine tune with a canopy that is already built and hard to move by oneself.
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post #2 of 7 (permalink) Old 01-18-2007, 11:06 PM
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have you tried droping the reflecter down to about 2-3 inches from the surface? i ran into the same problems as you when i set up my first planted tank about 4 years ago.
but im really just a begginer right now though sence i havent even done anything to my aquarium for like 2 1/2 years i have just let my plants grow.
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post #3 of 7 (permalink) Old 01-19-2007, 12:19 PM
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I don't have a formula, but distance from the water surface will effect the light in the tank. Higher will spread the light more, but dilute it.
I used 1" wood scraps stained the color of my hood. I placed them in between the reflectors, and canopy top.
1) lowered the lights,
2) allowed space to allow air to circulate and help cool.

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post #4 of 7 (permalink) Old 01-19-2007, 03:18 PM Thread Starter
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Thanks for the advice, but (don't shoot me) I do not use reflectors. I cannot find ones that will fit my lightstrips and as a result I would rather use more bulbs with higher lux readings than mess around. I do not have any issues with heat.

But my experiment is still young, so we will see.

I made my canopy out of pinewood. It is an easy wood to cut and work with to say nothing of the fact it is naturally light in colour, and reflects much of the light. I have not yet decided in coating the interior of the box with reflective material, but as I stated, I would rather add more strips.

I find however, that the idea of most advice being "watts per inch" or "watts per gallon" to be grossly misleading. The bulbs I use are distributed and sold by Hagen, and all are 40W. All have different spectrum readings (from 2800K to 18000K, the ones I like are 6700K) and different Lux readings (from 100 lux to 400 lux). So the idea that wattage equates to volume is wrong. Two bulbs can have the same wattage but entirely different lux readings, and the higher the lux, the more light one gets. Kind of like cars: may have the same horsepower, but different torque ratings tell you the real output capability of the engine.

The bulbs I like and use are 40W, 320 Lux 6700K. Seem to give a nice light.
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post #5 of 7 (permalink) Old 01-20-2007, 03:10 AM
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Without reflectors lights will spread out by the inverse square law with point sources of light (double the distance and quarter the intensity) with line sources like fluorescent tubes, I think the relationship is more like double the distance, half the power. One thing you can do is paint the inside of your canopy with white paint (use water washable paint for kitchen & bathroom use).

WPG is just a ballpark rule of thumb. Watts is a measure of the power the lights are consuming, not how much light they are producing. Since different light have different effeciencies, some conversion numbers have been mentioned in the past. For example WPG is based on T12 lighting. Typically T8 lighting is atleast 25% more effecient sou you can give yourself a 25% higher WPG number (just pulled that number out of the air, I dont remember the exacts off hand). Lux and Lumens arent the best rating for plants, as they are weighted towards human sight. This is why your daylight bulbs centered around 5,000-6,000K have higher ratings that bulbs farther from these numbers (with the same wattage). Most plant specific bulbs have a fairly low lumen/lux rating, but can grow plants very well. A higher lux or lumen rating does NOT mean the bulb is outputing more light, just that it will appear brighter to our eyes.

For a good read on this check out Luminous efficacy - Wikipedia, the free encyclopedia
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post #6 of 7 (permalink) Old 01-20-2007, 03:39 AM
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sorry for the thread jack but it's somewhat related

i have no idea if i'm asking this right but please bear with me. is it better to have 1 lamp or 2 lamps (or 3 or 4 etc etc) to obtain a certain wattage? like to have one 100watt lamp or two 50watt lamps. i believe the 100watt lamp gives you 100watts of intensity or something like that right, but the two 50watts will only give you 50watts of intensity? i remember reading it somewhere but can't find what that somewhere was anymore.
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post #7 of 7 (permalink) Old 01-20-2007, 03:48 AM
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WPG, Lux, Lumens, blah. Who really knows what they all mean, how to apply them properly to our tanks, and most of all, what our plants require? I think you'd be hard pressed to find many, if anyone, that does. So, let's look at some simple, general, factors.

You have a large tank that's 2' deep. That tells me you'll need either enough low intensity lighting to reach the bottom, or some intense lighting that will reach the bottom, usually achieved by good reflectors or point-source lighting (HQI). You are striking me as someone who simply wants a nice, simple planted tank to enjoy, and is not demanding of perfect aquascaping.

Let me ask you this: Are you or are you not dedicated to CO2 use? There is no half-assing here. It really is black or white. This will make a substantial difference in your lighting needs. Either way, you can acheive your desires, so don't let that decision influence you.

I prefer CO2. So let's start there (I will try to balance CO2/non-CO2 so that either way you go you will have good results). You are using 40w lights w/ no reflectors that are positioned high above the tank. While this can sustain plants, it probably won't grow them very well. I don't know your exact set-up, but if it's DIY, I would replace 2 of your 5 bulbs with T5HO's with good reflectors. So, you would have 3-40w NO bulbs to burn all day, with 2 T5's to run for about 6 hours per day on a timer. This sounds pretty good. You get to mix intensity with extended viewing pleasure. With non-CO2, you simply cut the photoperiod down--cutting the T5's down to 4 hours would probably do it. T5HO retro kits (or just parts) are very cheap. As for any algae woes, that would merit another thread.
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